Process for conversion of a cellulosic material

ABSTRACT

A process for the high temperature conversion of a cellulosic material into a bio-oil, wherein, under hydrogen atmosphere and in the presence of a catalyst, the cellulosic material is contacted in a reaction vessel with a liquid solvent, wherein water is present from 5% up to 80 wt %, based on the total amount of cellulosic material and liquid solvent present in the vessel, at an a controlled operating pressure of from equal to or more than 2.0 MPa to equal to or less than 13.0 MPa, wherein the partial hydrogen pressure contributes from equal to or more than 1.0 MPa to equal to or less than 6.0 MPa, and the total vapour pressure being lower than the autogenous pressure at the operating temperature and contributing in the range of from equal to or more than 1.0 MPa to equal to or less than 7.0 MPa, to produce a product mixture comprising bio-oil.

The present application claims the benefit of pending U.S. Provisional Application Ser. No. 62/270,063, filed 21 Dec. 2015, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a process for conversion of a cellulosic material and use of the products produced in such a process.

BACKGROUND TO THE INVENTION

With the diminishing supply of crude mineral oil, use of renewable energy sources is becoming increasingly important for the production of liquid fuels. These fuels from biological sources are often referred to as biofuels.

Biofuels derived from non-edible biological sources, such as cellulosic materials, are preferred as these do not compete with food production. These biofuels are also referred to as second generation, or advanced, biofuels. Most of these non-edible cellulosic materials, however, are solid materials that are cumbersome to convert into biofuels. A first step in conversion of these cellulosic materials is therefore a liquefaction of the cellulosic material into a liquid.

WO2013072383 describes a process for the conversion of a cellulosic material into a bio-oil, comprising the steps of contacting the cellulosic material with a liquid solvent in an inert atmosphere at a reaction temperature in the range from equal to or more than 260° C. to equal to or less than 400° C. to produce a product mixture; then separating a middle fraction from the product mixture, to produce a product mixture middle fraction; and recycling a first volume part of the product mixture middle fraction to be used as part of the liquid solvent; and using a second volume part of the product mixture middle fraction to produce a bio-oil. It was found that the addition of water in the feed and the removal of light and heavy products allows the build-up of bio-oil through consecutive refill of wood without severe increase in the by-production of heavy residual oil and the concomitant increase in oil viscosity.

Thus, water appears to favor the liquefaction process, i.e. water appears to be instrumental in depolymerizing the biomass. Therefore, at present, liquefaction of biomass is performed by using wet feedstock. Generally, liquefaction takes place in a high-pressure reactor, suitable for continuous operation, but possibly also in an autoclave or a similar pressure system. The presence of water in the liquefaction process results in high operating pressures (>80 bar) in the reactor system due to steam formation at high operation temperature, which generally is above 300° C. The high pressure in the sealed reaction system is the autogenous pressure, being the pressure that corresponds to the saturated vapor pressure above the solution at the specified temperature and composition of the solution (i.e. the natural pressure obtained upon heating the system).

Liquefaction processes may also comprise the presence of hydrogen in the process, for instance for use in catalytic hydrogenation of the biomass material. In the case of catalytic hydrogenation, an extra pressure component is added to the system: it is essential that a sufficiently high partial pressure of hydrogen is provided. This partial pressure of hydrogen is added to the autogenous vapor pressure of the reaction system, thus further increasing the total pressure.

However, high pressures require the use of high pressure reaction vessels and a feeding device that is suitable for feeding solids and/or slurries at high pressures. Alternatively, to avoid the pressures going up too high, pre-drying of the feedstock may be considered, however that requires additional equipment and energy consumption and results in lower yields or longer reaction times.

SUMMARY OF THE INVENTION

It would be advancement in the art to provide an economically attractive process for conversion of a cellulosic material, which allows the use of water and hydrogen in the liquefaction process while avoiding the above described drawbacks.

Such advancement has been achieved with the process according to the invention. According to the present invention, it has been found that wet biomass (in particular lignocellulosic) feedstock can be liquefied to bio-oil with a high oil yield at moderate pressure under aqueous conditions while also adding hydrogen in the presence of a catalyst. The advancement is achieved by allowing excess pressure to escape the liquefaction vessel. It was found that such pressure control did not have detrimental effect on oil yield, even though a reduction of the presently well-known beneficial effect of steam on the liquefaction process was expected to result in lower oil yields.

Accordingly, an embodiment provides a process for the high temperature conversion of a cellulosic material into a bio-oil, wherein, under hydrogen atmosphere and in the presence of a catalyst, the cellulosic material is contacted in a reaction vessel with a liquid solvent, wherein water is present from 5% up to 80 wt %, based on the total amount of cellulosic material and liquid solvent present in the vessel, at a controlled operating pressure of from equal to or more than 2.0 MPa to equal to or less than 13.0 MPa, wherein the partial hydrogen pressure contributes from equal to or more than 1.0 MPa to equal to or less than 6.0 MPa, and the total vapour pressure being lower than the autogenous pressure at the operating temperature and contributing in the range of from equal to or more than 1.0 MPa to equal to or less than 7.0 MPa, to produce a product mixture comprising bio-oil.

The process according to the invention allows a number of improvements when compared to prior art processes: to avoid the use of high pressure reaction vessels, to avoid the need for high pressure feeding devices, to avoid pre-drying the feedstock, while still delivering high oil yields.

DETAILED DESCRIPTION OF THE INVENTION

In the process, the operating pressure (also called the “set pressure”, being the pressure which was preselected as the pressure at which to carry out the reaction) is kept relatively low, being from equal to or more than 1.0 MPa (10 bar absolute) to equal to or less than 7.0 MPa (70 bar absolute). The operating pressure herein is: the sum of all vapour pressures in the system (i.e. including water) plus the partial pressure of hydrogen that is added to the system from external source. The sum of all vapour pressures in the system herein is defined as the “total vapour pressure”. This relates to the situation wherein the vapor pressure is saturated, i.e. when there is an equilibrium with the liquid phase. According to the invention the total vapour pressure is being kept lower than the autogenous pressure at the operating temperature. The autogenous pressure herein is defined herein as the highest pressure at a certain temperature that is measured in a reactor vessel, when a liquefaction reaction is carried at that temperature in a fully closed vessel in the absence of externally added hydrogen. Also here it is to be understood that the vapor pressure is saturated, i.e. when there is equilibrium with the liquid phase. Preferably, the operating pressure is from equal to or more than 3.5 MPa (35 bar absolute), preferably equal to or more than 4.2 MPa (42 bar absolute), more preferably equal to or more than 5.0 MPa (50 bar absolute), to equal to or less than 11.0 MPa (110 bar absolute), preferably equal to or less than 10.0 MPa (100 bar absolute), especially equal to or less than 9.0 MPa (90 bar absolute).

In an embodiment of the invention, the operating pressure of the reactor vessel is set such that the total vapour is less than 90% of the steam saturation pressure that corresponds to the operating reaction temperature applied, preferably <80%, more preferably <70%, more preferably <50% of the steam saturation pressure. For reference, the steam saturation pressure amounts to about 4 MPa and to about 8 MPa at 250° C. and 300° C., respectively, as can be found in engineering text books (CRC Handbook of Chemistry and Physics, 83^(rd) Ed., D. R. Lide (Ed.), 2003, p 6-10 to 6-11).

In another embodiment, the operating pressure is set such that the total vapour pressure is less than 90% of the autogenous pressure of the reaction medium, at the operating reaction temperature applied. Preferably, the operating pressure is set such that the total vapour pressure is at <80%, more preferably <70%, more preferably <50% of the autogenous pressure of the reaction medium. For reference, the use of a high-boiling liquid solvent such as guaiacol or methylnaphthalene at about 300° C. leads to a liquid solvent vapour pressure of 1-1.5 MPa, to which a steam saturation pressure of about 8 MPa, may add to constitute the largest part of the autogenous pressure, depending on water concentration.

Preferably, the total vapour pressure contribution to the operating pressure is in the range from equal to or more than 2.0 MPa (20 bar absolute), preferably equal to or more than 2.5 MPa (25 bar absolute), more preferably equal to or more than 3.0 MPa (30 bar absolute), to equal to or less than 6.0 MPa (60 bar absolute), preferably equal to or less than 5.5 MPa (55 bar absolute), especially equal to or less than 5.0 MPa (50 bar absolute).

Preferably, the partial hydrogen pressure contribution to the operating pressure is from equal to or more than 1.5 MPa (15 bar absolute), preferably equal to or more than 1.7 MPa (17 bar absolute), more preferably equal to or more than 2.0 MPa (20 bar absolute) to equal to or less than 5.0 MPa (50 bar absolute), preferably equal to or less than 4.0 MPa (40 bar absolute), especially equal to or less than 3.0 MPa (30 bar absolute).

The pressure may be controlled using any system known in the art. In an embodiment, the reaction vessel is provided with a pressure control system that opens a pressurization valve and shuts it once the internal pressure has reached a certain setpoint in the desired pressure range (“set pressure”). Depressurization occurs when the dump valve is opened. The valves may be used in an on/off operation rather than modulating, for cost reasons.

In another embodiment, the reaction vessel is equipped with an open gas restriction outlet that leads to a compartment of low but controlled pressure, e.g. atmospheric or near atmospheric pressure, which is also to be understood as being a pressure control system. The gas restriction outlet is designed such as to control the escape of gas via a pressure drop forced onto the restriction. The higher the pressure drop, i.e. the higher the pressure inside the reaction vessel, the higher the gas escape flow. The gas restriction outlet may be of fixed opening or adjustable opening as applied e.g. in flow-control valves.

In an embodiment, the process of the invention comprises condensing at least part of the reaction products and solvents including water exiting the reactor as vapour, into liquid components in a post reaction separator. Preferably at least 10%, more preferably at least 25%, most preferably at least 50% by weight of the total liquid feed (including solvent components and water provided as “fresh” feed, formed in the reactor or recycled to the reactor) exits the reactor in the vapour phase, such that the mass flow of liquid components out of the reactor is less than the feed by this amount.

In the process of the invention, the added hydrogen gas functions as “stripping” gas, this insures that hydrogen partial pressure is higher than it otherwise would be, by removing by vapour-liquid equilibrium the more volatile components of the feed, or formed from the feed. Thus, one can directly measure the “amount of stripping” of liquid components, taking for example the amounts of liquid at ambient temperature and pressure for feed (including any recycle or added solvent) vs. product from reactor, using room temperature and pressure as convenient condition for comparison.

The hydrogen referred to in the reaction of the current invention is “externally added” hydrogen, referring to hydrogen that does not originate from the cellulosic feedstock of the reaction itself, but rather is added to the system from another source, which may be any suitable source of gaseous hydrogen. Hydrogen is consumed in the high temperature conversion of the cellulosic material. Further, by controlling the pressure according to the invention, hydrogen also escapes the reaction system. However, the loss of hydrogen as a result of the escaping gas flow and the reaction is adjusted by adding extra hydrogen to the system to maintain the desired partial pressure of H₂.

The wording “high temperature conversion of a cellulosic material” as used herein may also be referred to herein as liquefaction, and the product mixture obtained may also be referred to herein as liquefaction product. In such a liquefaction process the cellulosic material is liquefied. By liquefaction (also herein referred to as liquefying) is herein understood the—at least partial—conversion of a solid material, such as cellulosic material, into one or more liquefied products.

By a liquefied product is herein understood a product that is liquid at ambient temperature (20° C.) and pressure (0.1 MPa) and/or a product that can be converted into a liquid by melting (for example by applying heat) or dissolving in a solvent. Preferably the liquefied product is a liquefied product that is liquid at a temperature of 80° C. and a pressure of 0.1 MPa. The liquefied product may vary widely in its viscosity and may be more or less viscous.

Liquefaction of a cellulosic material can comprise cleavage of covalent linkages in that cellulosic material. For example liquefaction of lignocellulosic material can comprise cleavage of covalent linkages in cellulose, hemicellulose and/or lignin present and/or cleavage of covalent linkages between lignin, hemicelluloses and/or cellulose.

As used herein, a cellulosic material refers to a material containing cellulose. Preferably the cellulosic material is a lignocellulosic material. A lignocellulosic material comprises lignin, cellulose and optionally hemicellulose.

Advantageously, according to the process of the invention, not only the cellulose is liquefied but also the lignin and hemicelluloses.

Any suitable cellulose-containing material may be used as cellulosic material in the process according to the present invention. The cellulosic material for use according to the invention may be obtained from a variety of plants and plant materials including agricultural wastes, forestry wastes, sugar processing residues and/or mixtures thereof. Examples of suitable cellulose-containing materials include agricultural wastes such as corn stover, soybean stover, corn cobs, rice straw, rice hulls, oat hulls, corn fibre, cereal straws such as wheat, barley, rye and oat straw; grasses; forestry products such as wood and wood-related materials such as sawdust; waste paper; sugar processing residues such as bagasse and beet pulp; or mixtures thereof.

Although wet feedstock may be used according to the process of this invention, the process may optionally comprise a pretreatment step comprising drying, torrefaction, steam explosion, particle size reduction, densification and/or pelletization of the cellulosic material before the cellulosic material is contacted with the liquid solvent. Such drying, torrefaction, steam explosion, particle size reduction, densification and/or pelletization of the cellulosic material may allow to adjust the amount of water present in the feedstock for improved process operability and economics.

Before being used in the process of the invention, the cellulosic material is preferably processed into small particles. Preferably, the cellulosic material is processed into particles having a particle size distribution with an average particle size of equal to or more than 0.05 millimeter, more preferably equal to or more than 0.1 millimeter, most preferably equal to or more than 0.5 millimeter and preferably equal to or less than 20 centimeters, more preferably equal to or less than 10 centimeters and most preferably equal to or less than 3 centimeters. For practical purposes the particle size in the centimeter and millimeter range can be determined by sieving.

If the cellulosic material is a lignocellulosic material it may also have been subjected to a pre-treatment to remove and/or degrade lignin and/or hemicelluloses. Examples of such pre-treatments include fractionation, pulping and torrefaction processes.

In another embodiment, before use in the process of the invention, the cellulosic material may be wet when introduced into the reaction vessel. Suitably, the cellulosic material may comprise from 2 wt %, preferably from 10 wt %, even more preferably from 25 wt % to 50 wt % of water based on the total amount of cellulosic material, when introduced into the reaction vessel. The cellulosic material may be dried or may be only partly dried to reach a preferred water content of 2 to 30 wt % based on the total weight of cellulosic material and liquid present in the reaction vessel. Optionally, the cellulosic material can be impregnated with water to reach the moisture content of 2 to 30 w %. In the case that the cellulosic material is wet when introduced into the reaction vessel, it may not be necessary to also add water to the system.

The amount of water in a cellulosic material may conveniently be determined by drying, for example according to ASTM-method D2216-98.

The catalyst used in the process of the invention is selected from Cr, Mo, W, Re, Mn, Cu, Cd, Fe, Co, Ni, Pt, Pd, Rh, Ru, Ir, Os, and alloys or any combination thereof, either alone or with promoters such as Au, Ag, Cr, Zn, Mn, Ni, Sn, Bi, B, O, and alloys or any combination thereof. The catalyst can also include a carbonaceous pyropolymer catalyst containing transition metals (e.g., chromium, molybdenum, tungsten, rhenium, manganese, copper, cadmium) or Group VIII metals (e.g., iron, cobalt, nickel, platinum, palladium, rhodium, ruthenium, iridium, and osmium). In certain embodiments, the catalyst includes any of the above metals combined with an alkaline earth metal oxide or adhered to a catalytically active support. The catalyst preferably includes a catalyst support material, selected from any suitable inorganic oxide material that is typically used to carry catalytically active metal components. Examples of possible useful inorganic oxide materials include alumina, silica, silica-alumina, magnesia, zirconia, boria, titania and mixtures of any two or more of such inorganic oxides. The preferred inorganic oxides for use as support material are alumina, silica, silica-alumina and mixtures thereof. Most preferred, however, is alumina. The catalyst used in the process of the invention is preferably sulfided according to methods known in the art. A preferred catalyst in the process of the invention is a sulfided catalyst comprising cobalt and molybdenum, optionally comprising a promoter, preferably a nickel-oxide promoter.

The process of the invention is carried out under hydrogen atmosphere. Preferably, hydrogen is bubbled through the reaction mixture, most preferably while being introduced from the bottom of the reactor vessel.

By a liquid solvent herein is understood a solvent that has a sufficiently low volatility to avoid the solvent being released through the system that is used to control the pressure. Suitably, the solvent should have a vapour pressure at the operating temperature that is lower than the set pressure/operating pressure, preferably at least 0.5, more preferably 1, particularly 1.5 MPa below the set pressure. Preferably, the solvent is liquid at a pressure of 0.1 MPa (1 bar absolute) and a temperature of 80° C. or higher, more preferably 100° C. or higher. Most preferably a liquid solvent is herein understood to be a solvent that is liquid at the reaction temperature and operating reaction pressure at which liquefaction is carried out. Hence, the liquid solvent is preferably a solvent which is liquid at a temperature in the range from equal to or more than 180° C. to equal to or less than 300° C. at a pressure of 0.1 MPa.

Preferably the liquid solvent is an organic solvent, which is herein understood to be a solvent comprising one or more hydrocarbon compounds. By a hydrocarbon compound is herein understood a compound that contains at least one hydrogen atom and at least one carbon atom, more preferably a hydrocarbon compound is herein understood to contain at least one hydrogen atom and at least one carbon atom connected to each other via at least one covalent bond. In addition to the hydrogen atom(s) and carbon atom(s) the hydrocarbon may contain heteroatoms such as for example oxygen, nitrogen and/or sulphur.

In a preferred embodiment the organic solvent comprises one or more carboxylic acids. By a carboxylic acid is herein understood a hydrocarbon compound comprising at least one carboxyl (—CO—OH) group. More preferably the organic solvent comprises equal to or more than 1 wt % carboxylic acids, more preferably equal to or more than 10 wt % carboxylic acids, most preferably equal to or more than 20 wt % of carboxylic acids, based on the total weight of organic solvent. There is no upper limit for the carboxylic acid concentration, but for practical purposes the organic solvent may comprise equal to or less than 90 wt %, more preferably equal to or less than 80 wt % of carboxylic acids, based on the total weight of organic solvent.

In another preferred embodiment the liquid solvent comprises at least one phenolic group, optionally with side groups such as alkyl- or alkoxygroups. Preferably, the liquid solvent comprises at least 1 wt % methoxyphenols, more preferably at least 10 wt % methoxyphenols, even more preferably at least 20 wt % methoxyphenols, based on the total weight of the liquid solvent.

In another embodiment the liquid solvent comprises paraffinic compounds, naphthenic compounds, olefinic compounds and/or aromatic compounds. Such compounds may be present in refinery streams such as gasoil and/or fuel oil.

The liquid solvent used in the conversion of the cellulosic feedstock comprises water in an amount of less than or equal to 80 wt %, preferably in an amount of less than or equal to 70 wt %, more preferably less than or equal to 60 wt %, and most preferably less than or equal to 50 wt %, based on the total weight of liquid solvent. Water may be present in the liquid solvent in an amount of more than or equal to 5 wt %, preferably more than or equal to 8 wt %, and more preferably in an amount of more than or equal to 10 wt %, based on the total weight of the liquid solvent. The water in the liquid solvent may for example be generated in-situ during the conversion.

In an embodiment of the invention, the process comprises recycling (a part of) the product mixture to be used as part of the liquid solvent. Evidently, that part of the product mixture also should have a vapour pressure at the operating temperature that is lower than the operating pressure as required for the liquid solvent. In the process of the invention, preferably at least part of the liquid solvent consists of a recycled product fraction. The liquid solvent preferably comprises equal to or more than 10 wt %, more preferably equal to or more than 20 wt %, even more preferably equal to or more than 30 wt %, still more preferably equal to or more than 50 wt %, most preferably equal to or more than 80 wt % and preferably equal to or less than 100 wt %, possibly equal to or less 90 wt %, based on the total weight of liquid solvent used in the conversion, of a recycled product fraction.

In an embodiment, for use in the liquefaction process, the recycled product may be mixed with one or more hydrocarbon compound(s) that are derived from a source other than the cellulosic material used as a feedstock, for example a hydrocarbon compound derived from a petroleum source (herein also referred to as fossil source).

In a further embodiment, the process of the invention comprises contacting the cellulosic feed material with a liquid solvent comprising recycled product and water.

The cellulosic material and the total liquid solvent (i.e. also including water) in the conversion process are preferably contacted in a liquid solvent-to-cellulosic material weight ratio of 2:1 to 20:1, more preferably in a liquid solvent-to-cellulosic material weight ratio of 3:1 to 15:1 and most preferably in a liquid solvent-to-cellulosic material weight ratio of 4:1 to 10:1.

The operating temperature at which the conversion of the cellulosic material is carried out according to the invention is in the range from equal to or more than 180° C. to equal to or less than 300° C. Preferably, the operating temperature is in the range from equal to or more than 190° C. to equal to or less than 275° C., more preferably in the range from equal to or more than 200° C. to equal to or less than 260° C. The operating temperature may also be a staged temperature profile, i.e. starting at a lower temperature for a certain period of time, followed by a higher temperature for another period of time. Preferably, a staged temperature profile comprises 1 hour at 200° C. and 4 hours at 250° C.

The process according to the invention can be carried out batch-wise, semi-batch wise, continuously and/or in a combination thereof. The process may for example be carried out in a continuously stirred tank reactor or in a plug flow reactor or a combination thereof. In a preferred embodiment, the process is carried out in a plug flow reactor.

Preferably, the residence time in any reactor for the conversion process lies in the range from equal to or more than 15 minutes, preferably equal or more than 30 minutes, more preferably equal to or more than 45 minutes, even more preferably equal to or more than 60 minutes; to equal to or less than 7 hours, more preferably equal to or less than 6 hours, even more preferably equal to or less than 5 hours, still more preferably equal to or less than 4 hours.

The product mixture may contain solids (such as unconverted cellulosic material and/or humins and/or char); liquids (such as water and/or hydrocarbon compounds); and/or gas.

The process of the invention advantageously allows one to produce a product mixture with a viscosity preferably in the range from 1 to 2000 centipoises (cP) at 30° C., more preferably a viscosity in the range from 1 to 1000 centipoises (cP) at 30° C., and most preferably a viscosity in the range from 2 to 500 centipoises (cP) at 30° C. As explained herein a middle fraction of the product mixture is recycled and used as part of the liquid solvent in the liquefaction process. Therefore the liquid solvent may also have a viscosity preferably in the range from 1 to 2000 centipoises (cP) at 30° C., more preferably a viscosity in the range from 1 to 1000 centipoises (cP) at 30° C., and most preferably a viscosity in the range from 2 to 500 centipoises (cP) at 30° C. The viscosity may depend on the number of recycles completed. For example, a product mixture respectively liquid solvent may comprise at least 10 wt %, more preferably at least 30 wt % and most preferably at least 50 wt % (based on the total weight of product mixture respectively liquid solvent) of a 3rd generation or higher generation reaction products and preferably have a viscosity in the range from 2 to 500 centipoises (cP) at 30° C., more preferably a viscosity in the range from 2 to 100 centipoises (cP); or for example a product mixture respectively liquid solvent may comprise at least 10 wt %, more preferably at least 30 wt % and most preferably at least 50 wt % (based on the total weight of product mixture respectively liquid solvent) of a 5th generation or higher generation reaction products and preferably have a viscosity in the range from 10 to 1000 centipoises (cP) at 30° C., more preferably a viscosity in the range from 20 to 500 centipoises (cP) at 30° C.

In an embodiment of the invention, after the (partial) conversion of the cellulosic material, the process comprises a subsequent step wherein the product mixture is separated into a light fraction comprising (hydrocarbon) compounds having a molecular weight of less than 100 grams per mol; a middle fraction comprising (hydrocarbon) compounds having a molecular weight in the range from equal to or more than 100 grams per mol to equal to or less than 1,000 grams per mol; and a heavy fraction comprising (hydrocarbon) compounds having a molecular weight of more than 1,000 grams per mol. The middle fraction may preferably be selected from the product mixture, to produce a fraction for use in recycling. The hydrocarbon compounds may also contain heteroatoms such as sulphur, oxygen and/or nitrogen.

The fractions may be separated from the product mixture using any kind of separation technique known by the person skilled in the art, including for example filtration, settling, fractionation (including atmospheric or vacuum distillation and/or flashing), centrifugation, cyclone separation, membrane separation and/or membrane filtration, phase separation, (solvent) extraction and/or a combination thereof. The product mixture middle fraction preferably comprises one or more oxygenates, more preferably two or more oxygenates. By an oxygenate is herein understood a hydrocarbon compound that contains at least one oxygen atom, more preferably by an oxygenate is herein understood a hydrocarbon compound further containing at least one oxygen atom bonded to a carbon atom via at least one covalent bond. Examples of oxygenates include hexanoic acid (boiling at about 205° C. at 0.1 MPa), pentanoic acid (boiling at about 186-187° C. at 0.1 MPA), levulinic acid (boiling at about 245-246° C. at 0.1 MPa), guaiacol (boiling at about 204-206° C. at 0.1 MPa), syringol (boiling at about 261° C. at 0.1 MPA) and/or gamma-valerolactone (boiling at about 207-208° C. at 0.1 MPa). Preferably the product mixture middle fraction is a fraction of which at least 90 wt % has a boiling temperature of equal to or more than 150° C. at 0.1 MPa and of which 90 wt % melts at a temperature equal to or less than the reaction temperature.

In a further embodiment the process comprises an additional step comprising hydrotreatment of at least part of the produced bio-oil. The hydrotreatment may for example comprise hydrogenation, hydrooxygenation and/or hydrodesulphurization using technologies and methods known in the art.

In a another embodiment the process according to the invention may further comprise a catalytic cracking step, preferably a fluidized catalytic cracking step, for example comprising contacting a feed comprising at least part of the bio-oil—which bio-oil may optionally have been hydrotreated—with a fluidized catalytic cracking catalyst at a temperature of equal to or more than 400° C., preferably a temperature in the range of equal to or more than 450° C. to equal to or less than 800° C., to produce one or more cracked products.

In the catalytic cracking step one or more cracked products are produced. In a preferred embodiment this/these one or more cracked products is/are subsequently fractionated and/or hydrotreated to produce one or more base fuels.

Such a base fuel may conveniently be blended with one or more other components to produce a biofuel or biochemical. Examples of such one or more other components include anti-oxidants, corrosion inhibitors, ashless detergents, dehazers, dyes, lubricity improvers and/or mineral fuel components, but also conventional petroleum derived gasoline, diesel and/or kerosene fractions.

By a biofuel is herein understood a fuel that is at least party derived from a renewable energy source. The biofuel may advantageously be used in the engine of a transportation vehicle.

EXAMPLES

The invention will now be further illustrated by means of the following non-limiting examples and comparative examples.

Examples 1-4

75-ml Parr5000 reactors were charged with a nominal 14 grams of tetrahydrofurfural alcohol, 6 grams of methoxypropylphenol, and 2 grams of deionized water. 0.12 grams of potassium carbonate was added as buffer, together with 0.35 grams of nickel-oxide promoted cobalt molybdate catalyst (DC-2534, containing 1-10% cobalt oxide and molybdenum trioxide (up to 30 wt %) on alumina, and less than 2% nickel), obtained from Criterion Catalyst & Technologies L.P., and sulfided by the method described in US2010/0236988 Example 5).

For each cycle of reaction, 2.0 grams of cellulosic floc (Leslie's Swimming Pool Supplies; nominal 200 microns) were added, followed by pressuring with varying amounts of hydrogen under stirring via stir bar. The reactor was heated to 190° C. for 1 hour, followed by 250° C. for 4 hours to complete the digestion and reaction of cellulose.

The process was repeated for 3 cycles of cellulose addition, with addition of sodium carbonate buffer as needed to maintain pH between 5-7. At the end of 3 cycles the reactor contents separated by filtration in a vacuum filter flask (Whatman GF/F paper). Recovered solids were negligible.

The aqueous product was analyzed by gas chromatography (“DB5-ox method”) using a 60-m×0.32 mm ID DB-5 column of 1 μm thickness, with 50:1 split ratio, 2 ml/min helium flow, and column oven at 40° C. for 8 minutes, followed by ramp to 285° C. at 10° C./min, and a hold time of 53.5 minutes. The injector temperature was set at 250° C., and the detector temperature was set at 300° C. A range of alkanes, ketone and aldehyde monooxygenates as well as glycol solvents and products, and polyols (glycerol) were observed, with volatility greater than C6 sugar alcohol sorbitol. GC measured products indicated a selectivity of 48% to products with volatility greater than sorbitol (C6 monomer), relative to the carbohydrate content of the digested portion of the wood initially charged.

For Examples 1-4, the initial hydrogen partial pressure was varied from 3.4 to 51 bar. The total GC wt % of observable products was observed to increase as the H₂ partial pressure was increased above 3.4 bar, with a maximum at 35 bar. The remainder of products was attributed for formation of heavy tars, which could not be eluted from the G.C.

TABLE 1 Yields from cellulose vs. H₂ partial pressure H₂ bar GC wt % 51.0 17.7 34.0 19.7 17.0 19.2 3.4 4.1

Example 5: Stripping Reactor Numerical Simulation

A process simulation model (Aspen Process Model V7.3) was created with a simulated wood feed composition (66% H₂O) and model reactions to form alcohol and phenolic products modelled by phenol, C₆-alcohol, glycerol, and ethanol products. The digester-reactor pressure was set at 41 bar, and temperature was set at 250° C. Following reaction, the vapour and liquid components were collected and cooled to 170° C. also at 41 bar, for separation in to vapour and liquid phases. The liquid phase contained only 8% by weight of water, but 41% phenol, 44% C6-alcohol and 5% glycerol. Solvent recycle was set at twice the wood feed flow, and the H₂ feed was varied to assess flowrate required to strip ethanol plus water vapour, and maintain a target H₂ partial pressure in the digester-reactor. A flowrate of 6 liters per hour (standard pressure and temperature) of hydrogen per gram/hour of wood feed, was enough to maintain a H₂ partial pressure of 35 bar in the digester reactor, relative to water vapour stripped.

This example demonstrates the use of H₂ stripping at a flowrate sufficient to maintain a high partial pressure of H₂ (35 bar) for a digester-reactor operated at 41 bar with liquid phase feed components which in the absence of stripping would contribute a vapour pressure in excess of 25 bar.

Examples 6-9: Microflow Stripping Reactor

A 0.5 inch outside diameter by 10-inch microflow reactor was packed with a bottom zone 2.5-inch zone of ⅛-inch Denstone support. 1.68 grams of crushed sulfided cobalt molybdate catalyst (as described in Example 1) were added on top of the support, followed by a 6.8 inch bed of comprising 6.9 grams of ground southern pine wood (52% moisture). The reactor was filled with a solvent of 90% tetrahydrofurfural alcohol in deionized water. 41 bar of H₂ backpressure was applied, and H₂ was sparged at the bottom of the reactor at 50 ml/min, as temperature was increased to 200° C. for 1 hour, followed by 250° C. for 4 hours, during which time fresh solvent mixture was added at 0.04 ml/min.

After 5 hours, a total of 23.57 grams of liquid product were collected via a product vessel separator on the vent gas line, relative to 16.1 grams of solvent fed. At the end of this run, the reactor was cooled, opened and an additional 6.04 grams of Southern pine wood were added, to replace that digested in cycle 1, along with 8.6 grams of solvent to replace the net amount stripped from the reactor.

This process was continued through 5 cycles of wood addition entailing 6.9, 6.04, 5.45, 5.69, and 5.31 grams of wood addition. Deinventory of the reactor after 5 cycles yielded 4.35 grams of undigested wood at 55% moisture content. Overall digestion was 85% of the total mass of wood injected for the 5 cycles of operation. GC analysis again revealed a range of GC observable products including ethylene glycol, propylene glycol, and ethanol. Total products observed were estimated as corresponded to greater than 50% of the conversion of the carbohydrate fraction of wood fed.

This example demonstrates the operation of a flow reactor with continuous stripping of hydrogen gas at a total pressure of 41 bar equal to the vapour pressure of water at the digester temperature employed (250° C.), under conditions where substantial liquid solvent (40-60%) was stripped beyond that provided as makeup liquid feed, and a majority (greater than 85%) of wood was digested to soluble products. 

We claim:
 1. A process for the high temperature conversion of a cellulosic material into a bio-oil, wherein, under hydrogen atmosphere and in the presence of a catalyst, the cellulosic material is contacted in a reaction vessel with a liquid solvent, wherein water is present from 5% up to 80 wt %, based on the total amount of cellulosic material and liquid solvent present in the vessel, at an operating temperature in the range from equal to or more than 180° C. to equal to or less than 300° C., and at a controlled operating pressure of from equal to or more than 2.0 MPa to equal to or less than 13.0 MPa, wherein the partial hydrogen pressure contributes from equal to or more than 1.0 MPa to equal to or less than 6.0 MPa, and the total vapour pressure being lower than the autogenous pressure at the operating temperature and contributing in the range of from equal to or more than 1.0 MPa to equal to or less than 7.0 MPa, to produce a product mixture comprising bio-oil.
 2. The process of claim 1 wherein the operating pressure is from equal to or more than 3.5 MPa, equal to or more than 4.2 MPa, to equal to or less than 11.0 MPa, preferably equal to or less than 10.0 MPa, wherein the partial hydrogen pressure contributes respectively from equal to or more than 1.0 MPa, to equal to or less than 5.0 MPa, and wherein the total vapour pressure contributes respectively in the range from equal to or more than 2.0 MPa, to equal to or less than 6.0 MPa.
 3. The process of claim 1 wherein the reaction vessel is provided with a pressure control system that opens a pressurization valve and shuts it once the internal pressure has reached a certain setpoint in the desired operating pressure range.
 4. The process of claim 1 wherein the reaction vessel is equipped with an open gas restriction outlet that leads to a compartment of low but controlled pressure.
 5. The process of claim 1 wherein the cellulosic material comprises from 2 to 50 wt % of water based on the total amount of cellulosic material, when introduced into the reaction vessel.
 6. The process of claim 1 wherein the catalyst is a sulfided catalyst comprising cobalt and molybdenum, optionally comprising a promoter.
 7. The process of claim 1 wherein liquid solvent has a vapour pressure at the operating temperature that is lower than the operating pressure.
 8. The process of claim 7 wherein liquid solvent is liquid at a temperature in the range from equal to or more than 180° C. to equal to or less than 300° C. at a pressure of 0.1 MPa.
 9. The process of claim 1 wherein the liquid solvent is an organic solvent.
 10. The process of claim 9 wherein the organic solvent comprises one or more carboxylic acids.
 11. The process of claim 9 wherein the organic solvent comprises paraffinic compounds, naphthenic compounds, olefinic compounds and/or aromatic compounds.
 12. The process of claim 9 wherein the organic solvent comprises at least one phenolic group, optionally substituted with side groups.
 13. The process of claim 1 wherein the process further comprises recycling a part of the product mixture having a vapour pressure at the operating temperature that is lower than the operating pressure, to be used as part of the liquid solvent.
 14. The process of claim 1 wherein the process further comprises a subsequent step wherein the product mixture is separated into a light fraction comprising compounds having a molecular weight of less than 100 grams per mol; a middle fraction comprising compounds having a molecular weight in the range from equal to or more than 100 grams per mol to equal to or less than 1,000 grams per mol; and a heavy fraction comprising compounds having a molecular weight of more than 1,000 grams per mol.
 15. The process of claim 14 wherein at least 30 wt % of the liquid solvent used in the conversion process consists of recycled product mixture middle fraction.
 16. The process of claim 2 wherein the operating pressure is from equal to or more than 4.2 MPa, to equal to or less than 10.0 MPa. 